Remediating RDX-contaminated water and soil using zero-valent iron

Soil and water contaminated with RDX (hexahydro-1,3,5-trinitro-1,3,5-triazine) pose a serious threat to the environment and human health. Our objective was to determine the potential for using zero-valent iron (Fe⁰) to remediate RDX-contaminated water and soil. Mixing an aqueous solution of 32 mg RDX L^-1 (spiked with ¹⁴C-labeled RDX) with 10 g Fe⁰ L^-1 resulted in complete RDX destruction within 72 h. Nitroso derivatives of RDX accounted for approximately 26% of the RDX transformed during the first 24 h; these intermediates disappeared within 96 h and the remaining ¹⁴C products were water soluble and not strongly sorbed by iron surfaces. When RDX-contaminated soil (30 mg RDX kg^-1 spiked with ¹⁴C-RDX) was treated with a single amendment of Fe⁰ (20 g kg^-1 soil) in a static soil microcosm, more than 60% of the initial ¹⁴C-RDX was recovered as ¹⁴CO₂ after 112 d. Treating surface and subsurface soils containing 3600 mg RDX kg^-1 with 50 g Fe⁰ kg^-1 at a constant soil water content (0.35-0.40 kg H₂O kg^-1 soil) resulted in a 52% reduction in extractable RDX following 12 mo of static incubation. A second Fe⁰ addition at 12 mo further reduced the initial extractable RDX by 71% after 15 mo. These results support the use of zero-valent iron for in situ remediation of RDX-contaminated soil.